Anyways, sometime this month or next month I'm supposed to be doing a placement at a computer tech store, and I've been there and the guys there sell refurbished computers with copies of XP - so yeah, it's going to be a while before XP itself stops being used in the mainstream sense.
I don't think it'll last until 2015 though. Microsoft will have made Windows 8 by then, and everyone will likely have switched to W7. It's very difficult to find a brand-new OEM system being sold with XP on it now (netbooks don't count). :P